In metrology, especially in process measuring technology, there are configurations in which a metallic body is mechanically coupled with a ceramic body. The mechanical coupling may in particular be an intermediate seal and/or a joint which is a welded, soldered or glued connection.
Due to the different coefficients of thermal expansion of, for instance about 16.5 ppm/K for the common stainless steels, 18.5 ppm/K for brass and, for example, 5 ppm/K to 8 ppm/K for ceramic materials, thermo-mechanical tension occurs in the area of influence of this mechanical coupling which may lead to drift or hysteresis of the measuring signal of a sensor connected with the body or the destruction of the mechanical coupling.
Elastic elements, such as elastomer gaskets or radially flexible metallic spring bodies positioned between metallic and ceramic bodies do have a certain decoupling effect, but on the other hand lead to other disadvantages.
Elastomers have a large coefficient of thermal expansion, which may lead to changeable axial tension and radial couplings in the clamping chain that depend on the algebraic sign of a temperature leap, as for example described in German patent DE 10 2009 027 899 A1.
A pressure sensor with a support ring having radially flexible spring struts has been described in German patent DE 196 28 551 B4. The disadvantage of this construction, however, is that the radial spring force coupled in a friction fit introduces bending torques into the measuring cell, which may be undefined due to relaxations leaps that occur.
Furthermore, from the European patent EP 0 995 979 B1 we know ceramic decoupling bodies between a ceramic pressure measuring cell and a metallic housing between metallic and ceramic bodies that may serve to decrease tensions, although in such cases hysteresis may occur depending on the possibility of relative movements to compensate thermal expansion differences.